之所以…是因为 / 之所以…是为了【zhīsuǒyǐ … shì yīnwèi / zhīsuǒyǐ … shì wèile】

之所以…是因为 reverses the order of 因为…所以: the result comes first, the reason second. The result is something the listener already knows; the reason is what the sentence is there to tell them. It is formal, at home in essays, speeches and interviews.

Compared with 因为…所以

Both say the same facts. 因为…所以 tells a story in order; 之所以…是因为 answers a "why" that is already in the air.

The second half

是因为 is the default. 是由于 is more formal. 是为了 gives a purpose instead of a cause.

In formal writing, 在于 "lies in" or 就在于 can replace 是因为.

之所以如此

With 如此 or 这样, the result is the whole situation just described, and the sentence explains it.

Common mistakes

The 是 is part of the frame; 因为 alone leaves it hanging. 之所以 already says "the reason", so it never pairs with 所以.

• × 我之所以没去，因为下雨了 → 我之所以没去，是因为下雨了
• × 我之所以没去，所以下雨了 → 我之所以没去，是因为下雨了

The subject goes before 之所以, and the cause never goes in the 之所以 half.

• × 之所以我学中文，是因为… → 我之所以学中文，是因为…
• × 之所以下雨，是因为我没去 → 我之所以没去，是因为下雨了